Razor blade and method of making same



United States Patent Office Patented June 30, 1970 3,518,110 RAZOR BLADEAND METHOD OF MAKING SAME Irwin W. Fischhein, Hyde Park, Mass., assignorto The Gillette Company, Boston, Mass., a corporation of Delaware NDrawing. Filed July 23, 1964, Ser. No. 384,805 The portion of the termof the patent subsequent to June 30, 1984, has been disclaimed Int. Cl.B26b 21/54 US. Cl. 117-93.4 11 Claims ABSTRACT OF THE DISCLOSURE Thisinvention relates to safety razor blades, either single edged or doubleedged, and pertains more specifically to an improved blade having on acutting edge an adherent coating of a selected type of fluorocarbonpolymer, which blade possesses unique shaving characteristics, and to amethod for making the same. The fluorocarbon polymer melts between 310C. and 332 C. and at 350 C. has a melt flow from 0.005 to about 600grams per ten minutes.

Although it has heretofore been proposed to improve the shavingcharacteristics of razor blades by applying to the cutting edges thereofadherent coatings of fluorocarbon polymers, and blades having suchcoatings have exhibited both improved shaving characteristics and longerlife, i.e. an increased number of shaves during which the same bladeexhibits acceptable shaving effectiveness, those blades which exhibitedoptimum effectiveness during the first shave have not exhibited maximumblade life.

The present invention, by making use of a fluorocarbon polymer havingspecial characteristics on the cutting edge of a razor blade in the formof an adherent coating having a thickness Within specified limits, makesit possible toachieve not only optimum effectiveness during the firstand succeeding shaves but also an unexpected extension of shaving lifebeyond that previously attainable.

The razor blades which may be treated in accordance with the presentinvention to provide the new blades having the improved and uniquequalities are from about 30 to 375 microns in thickness and havewedged-shaped cutting edges, the included solid angle of which isgreater than 14 and less than 35. Although the faces or sides of somesuch cutting edges extend back from the ultimate edge for a distance upto as much as 0.25 cm. or even more, it is not necessary that each facebe a single uninterrupted continuous surface or facet; it may insteadconsist of two or more facets formed by successive grinding or honingoperations and intersecting each other along zones generally parallel tothe ultimate edge. The final facet, i.e. the facet immediately adjacentthe ultimate edge, may have a width as little as 7.5 microns or evenless as compared to the diameter of a beard hair which averages about100 to 125 microns, while the thickness of the ultimate edge itself isgenerally less than 0.6 micron and preferably less than 0.25 micron.

The blade on which the coating of the present invention is applied maybe razor blade carbon steel or razor blade stainless steel such asUddeholm AEB or Sandvikens 11R51 or 12C27 or the like, or any otherrazor blade alloy steel. Uddeholm AEB stainless steel contains, inaddition to iron, 13% chromium, 1% carbon, 1% manganese, and 0.15%silicon. Sandvikens 11R51 contains, together with iron, 17% chromium, 8%nickel, 1.3% manganese, 1.2% silicon, 0.7% molybdenum, and 0.09% carbon.Sandvikens 12C27 contains, along with iron, 14%

chromium, 0.6% carbon, 0.3% silicon, and 0.3% manganese, However, thecoating may also be applied to blades having cutting edges of (or coatedwith) metals or metal alloys other than steel or stainless steel. Themetal is hardened by any suitable process, as by heattreating orworking. Although there is a limit to the extent to which the bladesubsequently may be heated, since excessive reheating Will lead to lossof hardness, some softening or tempering of the blades can be toleratedsince its disadvantages are more than offset by the improvement inshaving effectiveness produced by the invention.

The remarkable increase in shaving effectiveness manifested by theblades of the present invention is characterized by a decrease in pullas compared to uncoated blades; that is, a decrease in the forcerequired to cut the beard hairs, which becomes apparent in thenoticeably increased ease of shaving.

While the coating of solid fluorocarbon polymer may extend over theentire wedge faces back from the ultimate edge or even farther, it neednot cover the entire wedge faces. It may, for example, be confined to azone extending from the ultimate edge for a distance of only about 50microns. It need not cover that entire zone, but must cover a major partthereof, and although it need not extend to the ultimate edge itself, itmust extend at least to a micron or so from the ultimate edge. However,regardless of its extent, the thickness of the coating, within adistance of about 50 microns from the ultimate edge, must be from. about0.1 to about 0.3 micron, as measured by interference colors in whitelight as described in U.S. Pat. 2,937,976 assuming a refractive index of1.4.

Preferably, for optimum results, the coating must be continuous and ofthe aforesaid thickness from the ultimate edge for a distance of 50microns from the ultimate edge.

The solid fluorocarbon polymers which are effective in the practice ofthe present invention are those which melt between 310 C. and 332 C. andwhich have at 350 C. a melt flow rate from about 0.005 to about 600grams per ten minutes, as. measured before application to the blades.The beginning of melting is determined by the first appearance ofrounding of angular particle edges by visual observation at amagnification of diameters at a heating rate of 0.5 C. per minute; theend of melting is determined by the disappearance of birefringencebetween crossed polarizers at the same magnification and heating rate.Both the beginning and the end of melting for any given polymercomposition must be Within the range 310 C. to 332 C.

The melt flow rates specified herein were measured following theTentative Method of Test ASTM Designation: D 1238-57T published by theAmerican Society for Testing Materials as modified by R. E. Wiley in hisarticle published in the May 1961 issue of Plastics Technology at pages4548. All the measurements were made at 350 C. unless otherwisespecified and the extrusion pressure was 43.25 pounds per square inchusing a micromelt indexer constructed to the specifications in Wileyspaper made of 303 stainless steel with a Stellite orifice having alength of 0.1551 inch. Special care was taken to maintain the orifice at350 C. by means of an auxiliary heater. Measurements on very lowviscosity polymers were made using a plug to prevent premature flow fromthe extrusion orifice as described by Tordella et al., Modern Plastics31, 146 (1953). All of the flow rate values are reported as the numberof grams of material flowing through the orifice during a ten minuteperiod. The term melt flow rate as used in the specification and claimsis intended to have the foregoing meaning.

The preferred polymers are those which contain a chain of carbon atomsincluding a preponderance of CF --CF groups, such as polymers oftetrafiuoroethylene, including copolymers such as those with a minorproportion, e.g. up to 5% by weight of hexafiuoropropylene. Thesepolymers have terminal groups at the ends ofv the carbon chains whichmay vary in nature, depend ing, as is well known, upon the method ofmaking the polymer. Among the common terminal groups of such polymersare, -H, -COOH, -Cl, CCl

and the like. While the precise molecular weights and distribution ofmolecular weights of the preferred polymers is not known with certainty,it is believed that they have molecular weights ranging from about25,000 to about 500,000. The preferred chlorine-containing polymers arethose containing from 0.15 to 0.45% by weight of chlorine (which ispresent in the terminal groups). There may be used mixtures of two ormore fluorocarbon polymers, provided the mixtures have melt and meltfiow rate characteristics as specified above, even though the individualpolymers making up the mixture do not possess these characteristics. Itwill be appreciated that in the case of mixtures containing onecomponent of relatively low molecular weight, as well as in the case ofpolymers containing a fraction of relatively low molecular weight, partor all of the low molecular weight portion may evaporate during theheating or curing step to which the polymer coating is subjected afterapplication to the cutting edge, as described below. This evaporation ofa portion of the fluorocarbon polymer coating may result in a finishedcoating which has a melt flow rate different from that of the polymerinitially applied to the blade or even outside of the range specifiedabove.

The polymers are preferably applied to the cutting edges of the razorblades in the form of a dispersion of finely divided particles in aninert volatile liquid such as water, tert-butanol, or a perfluorinatedcyclic ether, or the like. For best results it is desirable that theparticle size of the dispersion be as small as possible, preferably from0.1 to 1 micron, any agglomerations of particles in the dispersion beingbroken up by subjecting the dispersion to the action of a homogenizershortly before application of the dispersion to the cutting edge.

The dispersion may be applied to the cutting edge in any suitable mannerto give as uniform a coating as possible, as, for example, by dipping orspraying; nebulization is especially preferred for coating the cuttingedges, in which case, an electrostatic field is preferably employed inconjunction with the nebulizer in order to increase the efiiciency ofdeposition. Preheat of the dispersion may be desirable to facilitatespraying, the extent of preheating depending on the nature of thedispersion, for example, in the case of a dispersion embodyingtert-butanol, preheating to a temperature of 35 C. may be desirable.Preheating of the blades to a temperature approaching the boiling pointof the volatile liquid may also be desirable.

In any event the blades carrying the deposited polymer particles ontheir cutting edges must be heated at an elevated temperature above themelting range of the polymer to form an adherent coating on the cuttingedge. The period of time during which the heating is continued may varywidely, from as little as a few minutes to as long as several hours,depending upon the identity of the particular polymer used, the natureof the cutting edge, the rapidity with which the blade is brought up tothe desired temperature, the temperature achieved, and the nature of theatmosphere in which the blade is heated. While the blades may be heatedin an atmosphere of air, it is preferred that they be heated in anatmosphere of inert gas such as helium, nitrogen, etc., or in anatmosphere of reducing gas such as hydrogen, or in mixtures of suchgases, or in vacuo. The heating must be sufficient to permit theindividual particles of polymer to coalesce and spread into asubstantially continuous film of the proper thickness and to cause it tobecome firmly adherent to the blade edge material.

The heating conditions, i.e. maximum temperature, length of time, etc.,obviously must be adjusted so as to avoid substantial decomposition ofthe polymer and/or excessive tempering of the metal of the cutting edge.Preferably the temperature should not exceed 430 C.

The following specific examples illustrate the nature of the presentinvention. The quality of the first shave obtained with blades of eachof the following examples is equal to the best quality obtained with thefluorocarbonpolymer-coated blades hitherto known; and the decrease inquality with successive shaves in the case of blades of each particularexample is less than the decrease in quality in the case of the bladespreviously known, i.e. the shaving life of the present blades is greaterthan that of those previously known, even when the latter blades weresuch that the quality of the initial shave was substantially inferior tothat of the present blades.

EXAMPLE 1 There was dispersed in a perfluorinated cyclic ether having amolecular weight of 416 (PC 75, Minnesota Mining and Manufacturing Co.),0.5% by weight of a finely divided solid polymer of tetrafiuoroethylenecontaining a minor proportion of chlorine and hydrogen atoms in theterminal groups (about 0.26% chlorine and about 0.01% hydrogen byweight) having a melting range from 318.5 C. to 323.5 C. as determinedvisually between crossed polarizers and melt flow rate measured at 350C. of 230 grams per ten minutes. This dispersion was sprayed by means ofa nebulizer onto the cutting edges of a stainless steel razor bladepreviously cleaned by thorough washing in trichloroethylene. The etherevaporated and the coated blade was then heated at 330 C. for fiveminutes in an atmosphere of hydrogen gas. The coating was substantiallycontinuous in the zone extending for a distance of about 50 microns fromthe ultimate edge and it had a thickness in that zone, as measured byinterference colors when viewed in white light at 750 diametersmagnification, from 0.12 to 0.27 micron.

EXAMPLE 2 There was prepared an aqueous dispersion containing 0.5 byweight of a polymer of tetrafiuoroethylene containing a minor proportionof chlorine and hydrogen atoms in the terminal groups (about 0.44%chlorine and about 0.06% hydrogen by weight). The polymer had a meltingrange of 318 C. to 324 C. and a melt flow rate at 350 C. of 300 gramsper ten minutes. There was employed as a stabilizer for the dispersion0.5% by weight of an alkylarylpolyether alcohol (Triton X-l00).Stainless steel safety razor blades were cleaned and preheated in air to99 C., then coated on their cutting edges with the foregoing dispersionby means of a nebulizer in a 40 kv. electrostatic field. The coatedblades, which dried almost immediately by evaporation of the water, werethen heated to 370 C. in five minutes in an atmosphere of hydrogen gasand were held at that temperature in the hydrogen atmosphere foreighteen minutes. The blades displayed a coating which was substantiallycontinuous throughout the zone extending about 50 microns from theultimate edge. The coating had a thickness throughout the zone ofapproximately 0.12 micron, when measured as in Example 1.

EXAMPLE 3 There was prepared in the cyclic ether of Example 1 adispersion of 1.0% by weight of a finely divided polymer oftetrafiuoroethylene containing a minor proportion of chlorine andhydrogen atoms in the terminal groups (about 0.18% chlorine and 0.02%hydrogen by weight). The polymer had a melting range of 320 C. to 325 C.and a melt flow rate at 350 C. of 40 grams per ten minutes. Thisdispersion was sprayed as described in Example 1 in a 40 kv.electrostatic field on the cutting edge of a stainless steel safetyrazor blade. The blade was then heated as described in Example 2. Theblade had a substantially continuous and uniform coating extending for adistance of about 50 microns from the ultimate edge, which coating had athickness of approximately 0.27 micron throughout the zone, whenmeasured as in EX- ample 1.

A carbon steel razor blade was coated in the same manner with the samedispersion except that the blade was heated in vacuo instead of inhydrogen. The finished blade had a coating substantially identical withthat produced on the stainless steel blade.

EXAMPLE 4 A polymer dispersion was prepared as described in Example 1,except that the polymer employed contained about 0.36% chlorine andabout 0.02% hydrogen by weight and had a melting range of 323.5 C. to326.5 C. and had a melt flow rate at 350 C. of 2.3 grams per tenminutes. This dispersion was applied to the cutting edge of a stainlesssteel razor blade, as described in Example 1, the blade was heated to370 C. in five minutes in an atmosphere of hydrogen gas and held at thattemperature in that atmosphere for eighteen minutes. The blade displayeda substantially continuous coating in the zone extending approximately50 microns from the ultimate edge and the coating had a thicknessranging from 0.12 to 0.27 micron throughout the zone, when measured asin Example 1.

EXAMPLE 5 Tetrafluoroethylene was polymerized in a diluent consisting ofa cyclic dimer of hexafiuoropropylene using ditertiary-butyl peroxide asa catalyst. The polymer contained terminal groups derived from thecyclic dimer and also contained in the terminal groups about 0.03%hydrogen by weight. The polymer had a melting range of 321.5 C. to325.5" C. and a melt flow rate at 350 C. of 2.2 grams per ten mintes. Adispersion of this polymer was prepared and applied to a stainless steelsafety razor blade as described in Example 1, except that the coatedblade was heated to a temperature of 370 C. in five minutes in anatmosphere of hydrogen gas and was held at that temperature for eighteenminutes in the same gas. The coating on the cutting edge of the bladewas substantially continuous in the zone extending from the ultimateedge for a distance of about 50 microns and the thickness of the coatingin that zone, was from 0.12 to 0.27 micron, when measured as in Example1.

EXAMPLE 6 A finely divided solid polymer of tetrafluoroethylenecontaining a minor proportion of chlorine and hydrogen atoms in theterminal groups (about 0.03% chlorine and 0.01% hydrogen by weight) witha melting range of 323.5 C. to 330.5 C. and :a melt flow rate at 350 C.of 0.4 gram per ten minutes was dispersed in the ether of Example 1 toform a 0.05% weight dispersion. This dispersion was sprayed by means ofa nebulizer and a 40 kv. electrostatic field onto the cutting edge of aclean stainless steel razor blade. The blade was heated to 370 C. infive minutes in a hydrogen gas atmosphere and held at 370 C. foreighteen minutes in this atmosphere. The blade displayed a continuouscoating in the zone extend ing from the ultimate edge for about 50microns, the coating having a thickness from 0.12 to 0.27 micronthroughout the zone, when measured as in Example 1.

EXAMPLE 7 A finely divided solid polymer of tetrafluoroethylenecontaining about 0.06% chlorine and 0.01% hydrogen by weight in theterminal groups with a melting range of 325 C. to 328.5 C. and ameltflow rate at 350 C. of 0.001 gram per ten minutes was mixed with anequal 6 Weight of a finely divided solid polymer of tetrafiuoroethylenecontaining about 1.0% chlorine and 1% hydrodrogen by weight in theterminal groups, with a melting range of 265 C. to 295 C. and a meltflow rate at 350 C. much greater than 600 grams per ten minutes. Themelting range of the mixture was 313.5 C. to 322.5 C. and the melt flowrate of the 50-50 solid mixture at 350 C. was 0.8 gram per ten minutes.This mixture was dispersed in the ether of Example 1 to form a 0.35% byweight dispersion which was sprayed by means of a nebulizer and a 40 kv.electrostatic field onto the cutting edge of a clean stainless steelrazor blade. The blade was heated to 370 C. in five minutes in ahydrogen gas atmosphere and held at 370 C. in that atmosphere foreighteen minutes. The blade displayed a coating like that of Example 6.

EXAMPLE 8 Tetrafluoroethylene was polymerized in aqueous dispersion withmethyl alcohol as the telogen using ammonium persulfate as the catalyst.The terminal groups of the polymer included hydroxymethyl and carboxylgroups. The polymer had a melting range of 323.5" C. to 328.5 C. and amelt flow rate at 350 C. of 0.008 gram per ten minutes. An aqueousdispersion containing 0.5% by weight of this polymer was prepared using0.1% by weight of an alkylarylpolyether alcohol as dispersing agent. Thedispersion was applied to the cutting edges of stainless steel razorblades as described in Example 2. The finished blades possessed asubstantially continuous coating on their cutting edges extending fromthe ultimate edge for a distance of about 50 microns, the thickness ofwhich was from 0.12 to 0.27 micron in that zone, when measured as inExample 1.

EXAMPLE 9 A dispersion was prepared as described in Example 1 of acopolymer of tetrafiuoroethylene with a small proportion ofhexafiuoropropylene (about 2.5% by Weight). The copolymer containedabout 0.1 chlorine and about 0.02% hydrogen by weight in the terminalgroups. The copolymer had a melting range of 320.5 C. to 328.5 C. and amelt flow rate at 350 C. of 0.1 gram per ten minutes. The dispersion wasapplied to the cutting edge of a stainless steel razor blade, cleaned asdescribed in Example l, by means of a nebulizer and employing a 40 kv.electrostatic field. The blade was heated to 370 C. in five minutes inan atmosphere of helium gas and held at that temperature in thatatmosphere for eighteen minutes. The blade possessed a substantiallycontinuous coating in the zone extending from the ultimate edge for adistance of about 50 microns, the coating having a thickness of 0.12 to0.27 micron in that zone, Where measured as in Example 1.

EXAMPLE 10 The polymer described in Example 3 was mixed with an equalweight of a finely divided solid polymer of tetrafluoroethylenecontaining about 1% chlorine and 1% hydrogen by weight in the terminalgroups, with a melting range of 265 C to 295 C. and a melt flow rate at350 C. much greater than 600 grams per ten minutes. The melting range ofthe mixture was 314 C. to 321.5 C. and the melt flow rate of the 5050solid mixture at 350 C. was 600 grams per ten minutes. This mixture wasdispersed in the ether of Example 1 to form a 0.5 by Weight dispersionwhich was sprayed by means of a neblizer and a 40 kv. electrostaticfield onto the cutting edge of a clean stainless steel razor blade. Theblade was heated to 370 C. in five minutes in a hydrogen gas atmosphereand held at 370 C. in that atmosphere for eighteen minutes. The bladedisplayed a coating like that of Example 9.

Although specific embodiments of the invention have been describedherein, it is not intended to limit the invention solely thereto, but toinclude all of the variations and modifications which suggest themselvesto persons skilled in the art.

What is claimed is:

1. A safety razor blade having on its cutting edge an adherent coatingconsisting essentially of a solid fluorocarbon polymer melting between310 C. and 332 C. and having at 350 C. a melt fiow rate from about 0.005to about 600 grams per ten minutes as defined herein, said coating beingcured in situ by heating above its melting range and having a thicknessfrom about 0.1 to about 0.3 micron in the zone extending from theultimate edge for a distance of about 50 microns.

2. A safety razor blade as claimed in claim 1 in which said polymercontains a chain of carbon atoms including a plurality of CF CF groups.

3. A safety razor blade as claimed in claim 1 in which said blade isstainless steel.

4. A safety razor blade as claimed in claim 3 in which said polymer is ahomopolymer of tetrafiuoroethylene.

5. A safety razor blade as claimed in claim- 3 in which said polymer isa copolymer of tetrafluoroethylene with up to 5% by weight ofhexafiuoropropylene.

6. A safety razor blade as claimed in claim 3 in which said polymercontains from 0.15 to 0.45% by weight of chlorine.

7. A method of making a razor blade which comprises depositing on itscutting edge a composition comprising a solid fluorocarbon polymermelting between 310 C. and 332 C. and having at 350 C. a melt flow ratefrom about 0.005 to about 600 grams per ten minutes as defined herein,and heating the deposited polymer to a temperature above its meltingrange to form an adherent coating on said cutting edge which has athickness from about 0.1 to about 0.3 micron in the zone extending fromthe ultimate edge for a distance of about 50 microns.

8. A method as claimed in claim 7 in which said heating is carried outin a reducing atmosphere.

9. A method as claimed in claim 7 in which said heating is carried outin an inert atmosphere.

10. A method as claimed in claim 7 in which said blade is stainlesssteel.

11. A method as claimed in claim 7 in which said deposition is carriedout by spraying in an electrostatic field.

References Cited UNITED STATES PATENTS 3,019,126 1/1962 Bartholomew11793.4 X 3,071,856 1/1963 Fischbein l17132 X 3,203,829 8/1965 Seyer etal. 117--132 3,283,117 11/1966 Holmes et al 117-1052 3,402,468 9/1968Kiss et al. 117--132 OTHER REFERENCES Brenner et al.: High TemperaturePlastics, 1962, Reinhold Pub. Corp., TP986A2B75, pp. 113-116.

RALPH S. KENDALL, Primary Examiner U.S. Cl. X.R.

